GPR, or ground-penetrating RADAR (where RADAR is “RAdio Detection and Ranging”), is a technology used to assess the composition and location of heterogeneous materials. GPR uses common radio frequencies and is particularly useful in that it is both non-destructive and non-ionizing. In fact, GPR uses frequencies similar to those of a cellular phone, but at far lower power levels. Common applications include locating the precise position of rebar (short for “reinforcing bar”) within a concrete wall/floor, identifying and locating buried objects underground, assessing the quality and uniformity of an asphalt or concrete highway surface, and detecting deterioration on bridge decks. In road surface applications, GPR is used, for example, to detect cracks, fissures, or contamination in any one of the chip seal, pavement layers, gravel base, and so forth. In many roadway applications, a resolution of features of the road surface of less than one inch (2.54 cm) is desired. Such systems may be mounted on vehicles, traveling over the surface while acquiring measurement data. GPR systems are disclosed in more detail in U.S. Pat. No. 5,499,029 to Bashforth, et al., and U.S. Pat. No. 5,384,715 to Lytton, which are hereby incorporated by reference.
For concrete measurements, GPR is used to locate metallic and non-metallic targets, as well as detect changes in the material properties and voids. Common surfaces include the walls, floors, ceilings, columns, and other support structures of buildings, parking garages, and bridges. Applications include mapping deterioration, water-ingress, verifying proper placement of reinforcements and tensioning cables, measuring slab thickness, and identifying areas in which the material can be safely drilled, cored, or cut.
Hand-held devices containing transducers are used to collect RADAR information. Current GPR imaging techniques produce data that are either 1) displayed as a screen image on the device, either in real-time or post processed, 2) recorded in electronic format for later playback processing, and interpretation, or 3) printed in real-time on some form of paper. In an example of the state of the art, one might attempt to find rebar (short for “reinforcing bar”), conduit, and post-tensioning cables in a concrete building before drilling into the building to carry out repairs or upgrades. In order to do so, one using GPR might pass a RADAR transducer over the surface and record the received response. Locations of targets may be directly interpreted and marked (using chalk or other marking device) at this point, or the information may post-processed for more sophisticated analysis. In either case, it is critical that the user is able to precisely register the location of the RADAR data with the recorded measurement file.
If concurrent or post-processing is performed, one creates a map of the measured surface, either on a computer and/or on a blueprint, with detected positions of buried targets. Then, using this map, one returns to the physical surface and pinpoints where the targets are found, and manually places chalk marks at the position of the rebar. Then, one cuts into the concrete or other surface at places away from the targets. Inaccuracy in this process could lead to accidental damage of critical structural elements within the concrete. For example, the destruction of a post-tensioning cable caused by drilling location that was improperly assessed, could render a parking garage structurally unsafe.
It is a further safety and ergonomic issue that the user(s) must simultaneously position the RADAR transducer while making accurate positioning marks on the measurement surface. In the case of walls and ceilings, this is clearly a two-handed or two-person operation. Two handed operation is generally unsafe while standing on a ladder.
While the above methodology currently used in the art works, it has obvious drawbacks. Such methods can be dangerous, time-consuming, which translates into extra costs of hiring personnel; more problematic, they can be inaccurate. The prior art relies largely on not only user interpretation of data, but user creation or manipulation of position-registered data. The greatest room for error is in manually drawing chalk marks on the physical structure. Any error in recording the location of the measurements or drawing the markings on the structure before drilling may have catastrophic consequences for the project. While careful planning, measurement, drawing, and execution of the above method prevents error, as noted above, safe techniques are time consuming and expensive.
An improvement in the prior art of GPR measurements is needed, in order to reduce hazards, expense, and time taken to analyze and/or prepare a surface for drilling, while increasing accuracy of the process.